Filter ventilators of the kind concerned here are known in the state of the art and are used primarily for ventilating the interiors of control boxes, circuit housings, and cases enclosing various other kinds of apparatus. In order to dissipate the heat generated by electronic control devices and other circuitry, a filter ventilator is used to introduce cold fresh air; this air is propelled through a hood mounted on a wall that separates the space to be ventilated from the exterior, is then passed through a filter positioned in an opening in this wall, and is finally expelled into the space that is to be ventilated by means of a blower situated behind said filter. In this process the function of the filter is to eliminate the dust in the cold air that is introduced, before it can reach the electronic components in the interior space. In particular electronic circuits in the vicinity of manufacturing and/or power-station installations are thus protected from rapid contamination by dust, which otherwise could cause short-circuiting and hence failure of the equipment, especially in humid environments. When filter ventilators are employed in very dirty surroundings, therefore, a regular exchange of the filter is essential to ensure a guaranteed cooling performance.
A customary prerequisite for the installation of a filter ventilator of this kind is that the space to be ventilated should be accessible from both the exterior and the interior. For instance, the blower situated inside the space, together with the filter, is inserted into the aperture in the wall from the interior of the space to be ventilated, and then it is fixed to the wall by operations conducted outside that space, whereas the hood positioned above it on the exterior side of the wall is mounted by means of operations on the inside. This kind of installation makes the process of exchanging the filter, which is situated between the blower and the hood, somewhat problematic; that is, at least the hood of the filter ventilator must be removed, which is an operation requiring considerable effort. Furthermore, when such activities are conducted in the interiors of control boxes, circuit housings or other cases for electronic apparatus, to ensure safety it is necessary for this apparatus to be turned off, which means that the machines and installations thereby controlled must also be inoperative during this time. For this reason, it is both laborious and expensive to exchange the filters of such a ventilator regularly.